Mysql Questions

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<pre>
<strong>40. What is InnoDB?
lnnoDB is a transaction safe storage engine developed 
by Innobase Oy which is a Oracle Corporation now.

41. How MySQL Optimizes DISTINCT?
DISTINCT is converted to a GROUP BY on all columns 
and it will be combined with ORDER BY clause.
SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;
SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;

42. How to enter Characters as HEX Numbers?
If you want to enter characters as HEX numbers, you can
enter HEX numbers with single quotes and a prefix of (X), 
or just prefix HEX numbers with (Ox).
A HEX number string will be automatically converted into 
a character string, if the expression context is a string.

43. How to display top 50 rows?
In MySql, top 50 rows are displayed by using this following query:
SELECT * FROM
LIMIT 0,50;

44. How many columns can be used for creating Index?
Maximum of 16 indexed columns can be created for 
any standard table.

45. What is the different between NOW() and CURRENT_DATE()?
NOW () command is used to show current year,month,date 
with hours,minutes and seconds.
CURRENT_DATE() shows current year,month and date only.

46. What are the objects can be created using CREATE statement?
Following objects are created using CREATE statement:
DATABASE
EVENT
FUNCTION
INDEX
PROCEDURE
TABLE
TRIGGER
USER
VIEW

47. How many TRIGGERS are allowed in MySql table?
SIX triggers are allowed in MySql table. They are as follows:
BEFORE INSERT
AFTER INSERT
BEFORE UPDATE
AFTER UPDATE
BEFORE DELETE and
AFTER DELETE

48. What are the nonstandard string types?
Following are Non-Standard string types:
TINYTEXT
TEXT
MEDIUMTEXT
LONGTEXT

49. What are all the Common SQL Function?
CONCAT(A, B) &ndash; Concatenates two string values to create a single 
string output. Often used to combine two or more fields into one single field.
FORMAT(X, D) &ndash; Formats the number X to D significant digits.
CURRDATE(), CURRTIME() &ndash; Returns the current date or time.
NOW() &ndash; Returns the current date and time as one value.
MONTH(), DAY(), YEAR(), WEEK(), WEEKDAY() &ndash; Extracts the given data 
from a date value.
HOUR(), MINUTE(), SECOND() &ndash; Extracts the given data from a time value.
DATEDIFF(A, B) &ndash; Determines the difference between two dates and it 
is commonly used to calculate age
SUBTIMES(A, B) &ndash; Determines the difference between two times.
FROMDAYS(INT) &ndash; Converts an integer number of days into a date value.

50. Explain Access Control Lists.
An ACL (Access Control List) is a list of permissions that is associated 
with an object. This list is the basis for MySQL server&rsquo;s security model 
and it helps in troubleshooting problems like users not being able to connect.
MySQL keeps the ACLs (also called grant tables) cached in memory. 
When a user tries to authenticate or run a command, MySQL checks 
the authentication information and permissions against the ACLs, in a 
predetermined order.                        </strong></pre>
                                    

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